Human immunodeficiency virus type 1 (HIV-1), a lentivirus etiologically linked to AIDS and related disorders, infects principally CD4+ T- lymphocytes and cells in the monocyte/macrophage lineage. In infected individuals, virus is found in peripheral blood monocytes/macrophage (PBMM), alveolar macrophage (AM), as well as in monocyte-related cells in the bone marrow, brain, and skin. The simian immunodeficiency virus isolated from Asian macaques, designated SIVmac, is a T-lymphocytopathic lentivirus that is genetically related to HIV-1 and HIV-2. SIVmac replicates in CD4+ lymphocytes and in cells in the monocyte/macrophage lineage. This virus causes a fatal AIDS-like disease in susceptible macaques. The hypothesis for the current proposal is that SIV mac infection of AM plays an important role in important role in pathogenesis. Infected monocyte/macrophage may account for viral persistence (and/or latency), and the cell activation state may influence the extent of viral replication and, ultimately, disease progression. The research in this proposal will evaluate the involvement of AM in SIV-infected animals (Specific Aims 1 to 3). This information will lay a basis for elucidating molecular mechanisms regulating cell activation and viral replication in AM (Specific Aims 4 and 5). SPECIFIC AIM 1: Optimal conditions will be established for recovery, characterization, and maintenance of rhesus macaque AM and PBMM in tissue culture systems. SPECIFIC AIM 2: AM and PBMM from SIV-infected macaques progressing through various disease stages will be tested in functional assays and cell surface markers will be characterized. SPECIFIC AIM 3: Replication of SIV will be monitored in AM and PBMM from infected macaques who progress from a healthy state to a fatal AIDS-like disease. The effects of cell activation on SIV replication will be analyzed and a role for macrophage in viral persistence (and/or latency) will be investigated. SPECIFIC AIM 4: An in vitro infection system for AM will be developed to analyze directly the effects of SIV on macrophage functions and to evaluate the role of cell activation on viral infection. SPECIFIC AIM 5: Transient expression assays will be performed with AM and macrophage tumor cell lines to elucidate molecular mechanisms regulating expression of both viral and macrophage genes. This proposal will examine the effects of SIV infection on AM in macaques with the goal of gaining a better understanding of the role of AM in individuals infected with HIV-1. Emphasis is directed at analyzing the consequences of viral infection on macrophage functions related to defense of the lung. With respect to pathogenesis, results of these investigations may reveal whether viral infection directly disrupts AM and PBMM or whether indirect mechanisms lead to cellular dysfunctions.